Nature of striation in 21 cm channel Maps: velocity caustics

ABSTRACT The alignment of striated intensity structures in thin neutral hydrogen (H i) spectroscopic channels with Galactic magnetic fields has been observed. However, the origin and nature these striations are still debatable. Some studies suggest that result solely from real cold-density filaments without considering role turbulent velocity shaping channel’s distribution. To determine relative contribution density forming channel maps, we analyse synthetic observations maps obtained realistic magnetized multiphase H i simulations thermal broadening included. We vary thickness apply Velocity Decomposition Algorithm to separate contributions. In parallel, GALFA-H compare results. Our analysis shows dominated by contribution, caustics mainly generate striations. show can cause a correlation between unsharp-masked far-infrared emission. demonstrate linear fibers revealed Rolling Hough Transform (RHT) originate caustics. As increases, fluctuations increases more RHT-detected tend be perpendicular field. Conversely, field is most prominent channels. conclude similar gradients (VChGs) approach, RHT traces through maps.